ISSN:0023-4753    

DOI:10.1002/crat.19790140902

出版商:WILEY‐VCH Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractThe notion of OD structures consisting of layers is explained, and visualization of its main features facilitated by a simple game: the player is asked to stack prefabricated layers periodic in 2 dimensions, which are all of the same kind or of a small number of different kinds, in accordance with some rules which correspond to the vicinity condition (VC).As shown, important features of the sequences of layers depend only on their symmetry (i.e. layer groups) and on geometrical features of any of the kinds of pairs, especially the layer group of any of the pairs.Table 1 shows that OD crystals consisting of layers occur amongst the most diverse chemical substances. In Tables 2 and 3 some examples of OD crystals with a variety of relations between crystallochemical entities and OD layers are listed.In the Appendix and Table 4 new and simplified formulae for the numberZv'(v)of possible positions of a certain layerLv′relative to the fixed position of its predecessor (or successor)Lvare give

ISSN:0023-4753    

DOI:10.1002/crat.19790140903

出版商:WILEY‐VCH Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractIt has been shown that the symmetry and structure of individual OD layers may depend on their actual stacking in a (polytypic) OD structure, leading to significant deviations from the ideal OD symmetry. This phenomenon has been called “desymmetrization of OD structures”; its significance for polytypism and for crystallochemistry is discus

ISSN:0023-4753    

DOI:10.1002/crat.19790140904

出版商:WILEY‐VCH Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractThe structures of pyroxenes are interpreted as OD structures consisting of layers.The symmetry relations of the idealized structures of “high pyroxenes”, consisting of only one kind of silicate sheets are described by the OD groupoid family:In this case the tetrahedral layers (OD layers) are identical with silicate sheets and the octahedral layers (OD layers) are identical with the chemical octahedral sheets, apart from the fact, that the O atoms are considered to belong partly to one and partly to the other idealized layer.In the idealized pyroxene structures, which are called in this paper “low pyroxenes”, every second silicate sheet is of lower symmetry. A silicate sheet of higher symmetry is considered as an OD layer, called tetrahedral layer. An OD layer of the other kind, called compound layer, consists of one silicate sheet of lower symmetry with an octahedral sheet attached to it on either side. With this definition of the two kinds of layers, the OD groupoid family has the following symbol:Polymorphism, disorder, twinning and parallel intergrowth are explained on thi

ISSN:0023-4753    

DOI:10.1002/crat.19790140905

出版商:WILEY‐VCH Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractThe OD groupoid family of the structure of dinitrosylcobalt chloride, [Co(NO)2Cl]2, is characterized by the symbol:The OD groupoid family of the structure is deduced from the observed arrangement of points in reciprocal space, the symmetry of the intensity distribution and the systematic absences. The structure is built of OD layers of one kind. The determination of the structure of the ordered orthorhombic form (MDO2) has been determined from Weissenberg data obtained by JAGNER and VANNERBERG refined with OD full‐matrix least‐squares methods, based on a total of 150 reflections and anisotropic temperature coefficients. AnRvalue of 0.13 has been obtained. The assumption of JAGNER that the structure is composed of dimers has been found to be justif

ISSN:0023-4753    

DOI:10.1002/crat.19790140906

出版商:WILEY‐VCH Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractThe relations between the groupoid of partial symmetry operations of an OD structure and the description of the symmetry of this structure by an OD groupoid family as well as parameters and the stacking of layers are discussed. Proposals are suggested for some changes in the symbols of the OD groupoid families in order to simplify and unify these symbols.

ISSN:0023-4753    

DOI:10.1002/crat.19790140907

出版商:WILEY‐VCH Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractX‐ray powder data of OD crystals may be misinterpreted, if the OD character of the substance is not taken into account. For some typical OD structures, problems in connection with their identification and the determination of lattice parameters are discussed. Some features of X‐ray powder patterns, which — on principle — are relevant to all OD crystals are sum

ISSN:0023-4753    

DOI:10.1002/crat.19790140908

出版商:WILEY‐VCH Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractDiethyl[5,6‐dichloro‐ 1,3‐benzodioxol‐(2)]‐phosphonate crystallizes in the triclinic space group P l̄ with two molecules per unit cell. The lattice parameters area= 11.716 Å,b= 8.471 Å,c= 7.644 Å; α = 82.47° β = 95.81°, γ = 95.89°. With X‐ray diffraction data collected on an automatic four circle diffractometer, the crystal structure was solved by direct methods and refined by least squares methods to anRvalue of 0.12 for 2374 measured reflections. The crystal used was im perfect. The substance is a derivative of acetales of formyl phosphoneacid esters. The aim is to find a correlation between the geometry of the s

ISSN:0023-4753    

DOI:10.1002/crat.19790140909

出版商:WILEY‐VCH Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractUsing X‐ray crystal structure analysis of the title compound the positions of all the atoms (including all H atoms) in the monoclinic unit cell with the parametersa= 13.900Å,b= 5.138Å,c= 17.956Å and β = 91.05° and the space group P 21/n were localized. The existence of an intramolecular N—H(N)…︁ O(1)‐bridge was inferred, whose H‐bridge acceptor predominantly is the π‐electron density of the carbonyl group. At the same time the H(N) atom participates in the intermolecular bridge NH(N)…︁ O′(1) to the symmetry‐equivalent neighbouring molecule. H‐bridge‐like interactions of the two phenyl hydrogen atoms H(6) and H(15) to the carbonyl oxygen O(2) have also been

ISSN:0023-4753    

DOI:10.1002/crat.19790140910

出版商:WILEY‐VCH Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractThe three‐dimensional structure of the title compound has been established by means of an X‐ray analysis. The product was formed by a thermal 1,3‐dipolar cycloaddition. According to the concerted [π4s+π2s]‐mechanism the formation of this stereoisomer should actually be forbidden. The structure determined by X‐ray analysis confirms the chemi

ISSN:0023-4753    

DOI:10.1002/crat.19790140911

出版商:WILEY‐VCH Verlag    

年代:1979

数据来源: WILEY